Bringing wireless indoors, which was once just a matter of antennas carrying a few cellular bands so people could get phone calls, has grown far more complex and demanding in the age of Wi-Fi, multiple radio bands and more powerful antennas.

DAS (distributed antenna systems) using coaxial cable have been the main solution to the problem, but they now face some limitations. To address them, Corning will introduce a DAS at this week's CTIA Wireless trade show in Las Vegas that uses fiber instead of coax all the way from the remote cell antennas to the base station in the heart of a building.

Cable-based DAS hasn't kept up with the new world, according to the optical networking vendor. Though Corning is associated more often with clear glass than with thin air, it entered the indoor wireless business in 2011 by buying DAS maker MobileAccess. That's because Corning thinks optical fiber is the key to bringing more mobile capacity and coverage inside.

The system, called Corning Optical Network Evolution (ONE) Wireless Platform, can take the place of a DAS based fully or partly on coaxial cable, according to Bill Cune, vice president of strategy for Corning MobileAccess. Corning ONE will let mobile carriers, enterprises or building owners set up a neutral-host DAS for multiple carriers using many different frequencies.

Though small cells are starting to take its place in some buildings, DAS still has advantages over the newer technology, according to analyst Peter Jarich of Current Analysis. It can be easier to upgrade because only the antennas are distributed, so more of the changes can be carried out on centralized gear. Also, small cells are typically deployed by one mobile operator, and serving customers of other carriers has to be done through roaming agreements, he said.

However, some DAS products based on coaxial cable are limited in how they can handle high frequencies and MIMO (multiple-in, multiple-out) antennas, Jarich said. Some vendors are already promoting fiber for greater flexibility and capacity, he said.

Going all fiber -- up to the wireless edge, at least -- will make it easier and cheaper for indoor network operators to roll out systems that can deliver all the performance users have come to expect from wireless networks, according to Corning. That includes more easily adding coverage for more carriers, as well as feeding power and data to powerful Wi-Fi systems that can supplement cellular data service, the company says.

Wireless signals don't travel the same way inside buildings as they do outdoors, so one antenna can't always cover the interior, regardless of whether it's mounted in the building or on a nearby tower. A DAS consists of many antennas spaced throughout a structure, all linked to a base station in a central location. Most types of DAS use coaxial cable to carry radio signals in from the distributed antennas.

However, those copper cables get more "lossy" as the frequencies they have to carry get higher, meaning they lose a lot of their signal on the way to the base station, Corning's Cune said. That has left coax behind as new frequencies are adopted, he said. For example, coax isn't good at carrying the 5GHz band, which is crucial in newer Wi-Fi equipment, Cune said.

MIMO, a technology that uses multiple antennas in one unit to carry separate "streams" over the same frequency, is another big limitation of DAS, according to Corning. MIMO antennas for better performance can be found in newer Wi-Fi gear based on IEEE 802.11n and 802.11ac, as well as in LTE. A coax-based DAS with MIMO antennas needs to have a separate half-inch-wide cable for every stream, which is a major cabling challenge, Cune said.

Corning ONE links each antenna to the base station over optical fiber, converting the radio signals to optical wavelengths until they reach the base station. Fiber has more capacity than coax, can handle higher frequencies, and requires just one cable from a MIMO antenna, Cune said. Because of fiber's high capacity, it's relatively easy to bring other mobile operators onto the DAS.

The system is based on optical fiber, but it can be extended over standard Ethernet wiring to provide backhaul for Wi-Fi access points. Each Corning ONE remote antenna unit that's deployed around a building will have two Ethernet ports to hook up nearby Wi-Fi access points, which can use the fiber infrastructure for data transport to wired LAN equipment, Cune said.

Corning ONE is in beta testing at one enterprise and will have limited availability beginning in late June, after which orders can be placed, Cune said. It is expected to be generally available two to three months later. The company expects its main customers to be mobile operators, though most of those operators will arrange multi-carrier services, he said. Enterprises and large building owners increasingly will step in to buy and deploy the DAS, Cune said.